If John was none of the great figures they expected, the Pharisees wanted to know what right he had to baptize. Barnes explains that the Pharisees "were very tenacious of rites and customs, of traditions and ceremonies," and believed new rites could be added only by the authority of a prophet or the Messiah. Gill says they thought no one ought to practice this "unless he was the Messiah, or his forerunner, or some eminent prophet." Matthew Henry writes, "It is taken for granted that Christ, and Elias, and that prophet, would baptize, when they came to purify a polluted world." Their question was a challenge to John's authority.

John did not defend his credentials. He pointed to Someone else: "I baptize with water: but there standeth one among you, whom ye know not; He it is, who coming after me is preferred before me, whose shoe's latchet I am not worthy to unloose" (John 1:26-27). The next day he named that One: "Behold the Lamb of God" (John 1:29). Then he gave the reason for his baptizing in plain words: "that he should be made manifest to Israel, therefore am I come baptizing with water" (John 1:31). His authority came from "he that sent me to baptize with water" (John 1:33).

Barnes says that baptizing a convert from paganism was common before John, "but it was not customary to baptize a 'Jew.'" Gill disagrees, saying the baptism of proselytes "seems to be of a later date than this." John was calling Jews themselves to be baptized, which is why his practice drew official attention. Gill notes that "the Jews expected that baptism would be administered in the times of the Messiah, and his forerunner," though where the idea came from "it is not easy to say." He reports that Grotius traced it to Zechariah 13:1 ("a fountain opened... for sin and for uncleanness") and Lightfoot to Ezekiel 36:25 ("Then will I sprinkle clean water upon you").

The "shoe's latchet" (John 1:27) is the strap of a sandal; untying it was a servant's task. The KJV says those sent "were of the Pharisees" (John 1:24), while the ESV reads "they had been sent from the Pharisees."

The Pharisees asked about John's authority; John answered by pointing to Christ. Even John's baptism was not about John. It existed so that Jesus "should be made manifest to Israel" (John 1:31). God Himself had sent John to baptize and had told him how he would recognize the One who "baptizeth with the Holy Ghost" (John 1:33).

The same question about John's authority came back later, when Jesus asked the leaders, "The baptism of John, whence was it? from heaven, or of men?" (Matthew 21:25). The Gospel's answer is clear: John was "a man sent from God" (John 1:6).